In the extrusion of metals (for example aluminum, brass, bronze, etc.) into length of a desired profile, very hot billets (in the order of about 500 degrees C. for aluminum) are loaded into the extrusion press for squeezing through the die;
For aligning, guiding and feeding the billet to, and through, the die the extrusion press comprises a hollow tubular container before the die, co-axial with the die and having an internal diameter greater (about 375/1000") than the outer diameter of the billet and a stem of lesser diameter than the diameter of the container tube co-axially aligned with the die and reciprocal from a position remote, to a position proximate, the die. Disposed intermediate the billet and stem is a dummy block loaded behind the billet when the billet is loaded and of substantially the same diameter as the central bore of the container (about 20/1000" clearance exists between the inner wall defining the bore of the container and dummy block) for engagement with the butt end of the billet for squeezing the billet through the die while substantially precluding back extrusion. The press includes a chute below the container adjacent the die so that when the stem is reciprocated away from the press, and the butt end of the billet is guillotined from the face of the die, the dummy block and butt end drop into the chute for manual removal at a remote station. The dummy block and butt end of the billet are then manually separated, the dummy block returned for reuse, and the butt end recovered for scrap. The above procedure is repeated for each billet, each repetition of the procedure requiring separate manipulation, and manhandling of each dummy block;
Attempts have been made to fix the dummy block permanently to the stem to save time, labour and back injuries. However, during the extrusion process a thin layer of billet metal builds up on the interior container wall defining the bore, decreasing the internal diameter of the container. Therefore, when the dummy block is retracted with the stem, the outer edge of the dummy block scrapes the thin layer of metal from the wall jamming the dummy block in the container and damaging the dummy block or container. The press must then be temporarily shut down for parts replacement or repair;
An attempt has been made in U.S. Pat. No. 3,303,684 to provide an expandable fixed dummy block of substantially the same diameter as the bore of the container for passage through the container when pushing a billet towards the die, but of reduced diameter when retracted;
The fixed dummy block disclosed is normally smaller than the container tube and presents a flat annular ring of metal at the periphery of the block surrounding a central curved dished portion, the flat annular ring for engagement with the butt end of the billet. As pressure is brought to bear against the butt end of the billet, the radius of curvature of the dished portion changes to flatten the dish and expand the effective diameter of the face of the fixed dummy block to substantially seal the container tube as the billet is squeezed through the die and preclude back extrusion past the dummy block to the stem. However, because of the fixed dummy block's dished configuration, as the billet is pushed forward to the fixed dummy block, billet metal collects in the dished portion reducing by an additional percentage, depending on the curvature of the dished portion, the total metal that may be extruded from each billet. When weights of metal in excess of millions of pounds are extruded each year, any additional percentage of waste or scrap metal increases costs substantially. Furthermore, no degree of control of the expansion of the diameter of the dummy block is provided resulting in uncontrolled expansion which in some instances could cause the fixed dummy block to seize against the inner wall of the tubular container;
It is therefore, an object of this invention to provide an expandable fixed dummy block which minimizes wastage of metal during the extrusion process and whose diameter changes can be controlled to control the expansion of the face of the dummy block;
Further and other objects of the invention will be realized by those skilled in the art from the following summary of the invention and detailed description of a preferred embodiment thereof.